The invention relates to hydrotalcite-like compositions useful as halogen scavengers in polymer formulations. More particularly, the invention related to the use of aluminum magnesium hydroxy carbonate solid solutions that inhibit the adverse effect of halide catalyst residues in plastics.
In general during the preparation of various synthetic polymers the catalyst, used in the preparation or at least the residue thereof almost invariably remains in the final product. The removal of this catalyst residue substance, which may be present at levels as low as ten parts per million, is commercially impractical. However, leaving the catalyst in the polymer, even at such low concentrations, often causes problems.
The catalysts used to polymerize olefinic monomers are typically halogen-containing metallic or organometallic compounds, e.g., Ziegler-Natta catalysts containing titanium tetrachloride. It is reported that residual titanium chloride species in the polymers interfere with the functioning of stabilizers, e.g., antioxidants, that are typically compounded with the polymer. Residual catalyst may also catalyze polymer degradation reactions, and, particularly with halogen-containing catalyst residue, the halogens can promote corrosion of the equipment used to compound and process the polymer.
Polymers that have been compounded with stabilizers, particularly thermal and light, stabilizers, exhibit a discoloration, i.e., they develop a yellow or pinkish coloration. This has been attributed to the action of residual catalyst, and particularly halide ions, reacting with the stabilizers that have a phenol or a quinone functional group. The halide may react with the phenol group to generate a colored phenolate anion.
Since most residual catalysts are acidic, an approach to overcoming the problems associated with residual catalyst is to add a basic material to the polymer, to thereby neutralize the residual catalyst. Basic materials for this purpose are known in the art, and are commonly referred to as neutralizer compounds or halogen-scavenging compounds. One class of halogen-scavenging compound is hydrotalcite and hydrotalcite-like materials.
Hydrotalcite is the name given to a natural mineral having the chemical structure Al2Mg6OH16(CO3).4H2O, which may also be written as Al2O3.6MgO.CO3.12H2O. Natural hydrotalcite is an example of a basic magnesium alumino-carbonate hydrate. As obtained from the earth, natural hydrotalcite is generally contaminated with other minerals such as penninite and muscovite, as well as various heavy metals. The impurity levels in natural hydrotalcite, as well as its scare occurrence around the world, have limited its commercial use giving use to the preparation of purified synthetic hydrotalcite. For example, U.S. Pat. No. 5,250,279 describes a method for the preparation of high purity synthetic hydrotalcite having a small platelet morphology by reacting a mixture of a magnesium source, such as magnesium oxide, with an alkali metal bicarbonate, solid alumina trihydrate and an alkali metal aluminate under aqueous hydrothermal conditions at a temperature of about 160-200xc2x0 C. Preparation of synthetic hydrotalcite said to have a composition which matches natural hydrotalcite is found in, for example, U.S. Pat. Nos. 3,650,704 and 3,539,306.
The term xe2x80x9chydrotalcitexe2x80x9d refers to a class of basic aluminum magnesium carbonate compounds or complexes having various lattice structures and compositions.
U.S. Pat. No. 4,284,762 (the ""762 patent) for example discloses a hydrotalcite of the formula
Mg1-xAlx(OH)2Ax/nnxe2x88x92omH2O
wherein x is greater than 0 but less than or equal to 0.5, m is a positive number, and Anxe2x88x92 represents an anion having a valence of n, or a product resulting from the surface-coating of said hydrotalcite with an anionic surface-active agent. The hydrotalcite has a BET specific surface area of not more than 20 m2/g, and a crystallite size, in the  less than 003 greater than  direction of at least 600 xc3x85, and preferably at least 1,000 xc3x85.
U.S. Pat. No. 4,299,759 (the ""759 patent) discloses a hydrotalcite of the same composition as set forth in the ""762 patent, but having a BET specific surface area of not more than 30 m2/g. The ""759 patent discloses that the surface treatment, i.e., the addition of sodium stearate to the hydrotalcite particle, can be achieved by adding an aqueous solution of sodium stearate to a suspension of the hydrotalcite powder to cause chemical adsorption of the surface-active agent to the surface of the solid powder. The surface treatment agent is preferably present at a loading of about 1 to about 10% by weight, based on the weight of the hydrotalcite.
U.S. Pat. No. 4,560,545 relates to a process for preparing a basic aluminum magnesium carbonate of the formula
Al2.Mg6.(OH)14.(CO3)2.4H2O.
The process comprises heating an aqueous slurry of aluminum hydroxide, magnesium hydroxide and either ammonia or a water-soluble organic nitrogen-containing base, in the presence of carbon dioxide and at a temperature of between 70 and 100xc2x0 C. at atmospheric pressure. The reaction time is from 1 to 12 hours, and the carbon dioxide is bubbled through the slurry during this time. The basic aluminum magnesium carbonate so produced may be used in pharmaceutical compositions.
Hungarian Patent HU 30,453 (Abstract No. 101:43635g, prepared by the Chemical Abstracts Service) discloses a composition with the formula
Al2.Mg4.(OH)12.(CO3).2H2O.
The composition is prepared by the reaction of MgCl2 with Na2CO3 and Na orthoaluminate or Al(OH)3 in the presence of NaOH.
U.S. Pat. No. 4,539,195 claims a crystalline basic aluminum magnesium carbonate of the formula:
Al2(Mg)6(OH)12(CO3)3.x(H2O)
in which xxe2x89xa74, obtainable by hydrothermal reaction of aluminum hydroxide with magnesium hydroxide or magnesium oxide in the presence of carbonate ions in stoichiometric amounts under the influence of gravitational forces at a temperature of 50 to 100xc2x0 C.
A basic magnesium aluminum carbonate of the formula
Al2O3.xMgO.yCO2.zH2O
is described in British Patent 1,086,779, wherein x can be 0.15 to 1.5, y can be varied from 0.3 to 2.5, and z is not less than 2.5.
U.S. Pat. No. 4,675,356 discloses a hydrotalcite solid solution represented by the following formula
[(M12+)y1(M22+)y2]1-xMx3+(OH)2Ax/nnxe2x88x92.mH2O
wherein M12+ represents at least one divalent metal selected from the group consisting of Mg, Ca, Sr and Ba; M22+ represents at least one divalent metal cation selected from the group consisting of Zn, Cd, Pb and Sn; M3+ represents a trivalent metal cation, Anxe2x88x92 represents an anion having a valency of n, and x, y1, y2 and m are positive numbers represented by the following expressions 0 less than xxe2x89xa60.5, 0 less than y1, 0 less than y2, 0.5xe2x89xa6y1+y2 less than 1, and 0xe2x89xa6m less than 2; and to a resin composition comprising the above agent. The hydrotalcite of the ""356 patent may be surface treated with, for example, anionic surface-active agents such as sodium stearate.
Reheis, Inc., Berkeley Heights, N.J., sells an aluminum magnesium hydroxy carbonate, trademark L55-R(copyright), having an analysis of 14-18% aluminum oxide, 25-29% magnesium oxide, 15-19% sodium stearate and 8.5-13.5% carbon dioxide. L55-R(copyright) is a white, odorless powder having a bulk density of 0.19-0.35 g/cc and a particle size of 100% through 400 mesh (37 microns) and not less than 90% through 10 microns.
While the prior art describes several hydrotalcite and hydrotalcite-like materials, there remains a need in the art for a system in which the modification of polymeric materials, results in substantially eliminating the problems associated with residual catalyst, and other halide-generating mechanisms, in the polymer.
The present invention provides a solid solution having the formula Al2(Mg)a(OH)b(CO3)c(G)d.eH2O wherein 3xe2x89xa6axe2x89xa65.5; 8xe2x89xa6bxe2x89xa614; 1.2xe2x89xa6cxe2x89xa63; 0xe2x89xa6dxe2x89xa61; 1xe2x89xa6exe2x89xa610 and G is a surface active agent which when incorporated in olefin polymers and copolymers substantially eliminates the adverse corrosion and discoloration of these polymeric materials that otherwise results from the residual halogen catalyst content. The solid solution has a crystallite size in the  less than 003 greater than  direction of about 190 xc3x85 to about 225 xc3x85, and has bidentate coordination for carbonate ion as shown by an infrared spectrum. Preferably, the surface active agent is a metal salt of a C10-C22 saturated fatty acid, and more preferably is sodium stearate, zinc stearate or calcium stearate. In a preferred embodiment, the solid solution has the above formula wherein 4.1xe2x89xa6axe2x89xa65.3; 10xe2x89xa6bxe2x89xa612; 1.3xe2x89xa6cxe2x89xa63; 0.05xe2x89xa6dxe2x89xa60.5; 3xe2x89xa6exe2x89xa69.
That the solid solution has bidentate coordination for the carbonate ion can be seen by a split absorption band in the region of 1415-1480 cmxe2x88x921. The solid solution preferably has a BET specific surface area of about 25 m2/g to about 40 m2/g. The solid solution may be present in an aqueous slurry, although preferably it is a dry powder. The dry powder has a tap density of about 0.1 g/cc to about 0.3 g/cc. In inhibiting the corrosion-causing tendency and coloration of halogen-containing olefin polymers or copolymers, about 0.01% to about 1% of the solid solution is incorporated into an olefin polymer or copolymer.
The solid solution, having surface active agent, may be formed by a process wherein an aqueous slurry comprising an aluminum compound, preferably basic aluminum carbonate gel and/or aluminum hydroxide, and a magnesium compound, preferably basic hydrated magnesium carbonate and/or magnesium oxide, wherein the molar ratio of magnesium to aluminum is about 1.5 to 2.75, is heated to a temperature of about 70xc2x0 C. to about 95xc2x0 C. and for a reaction time xe2x80x9cXxe2x80x9d to provide a first slurry, where xe2x80x9cXxe2x80x9d is a period of time sufficient to achieve removal of substantially all free and loosely bound carbon dioxide from the aqueous slurry. Then at least one surface active agent is added to the first slurry, to provide a second slurry. The second slurry is heated to a temperature of about 125xc2x0 C. to about 140xc2x0 C. for a time sufficient for a suspension test to be passed. The suspension test is described later herein.
When magnesium oxide is the magnesium compound in the above process, aluminum hydroxide is preferably the aluminum compound, and a stream of carbon dioxide gas is passed through the second slurry at a rate sufficient to produce a solid solution. When basic aluminum carbonate gel is the aluminum compound, it preferably has an Al2O3 content of about 2% to about 20% by weight. When magnesium carbonate is the magnesium compound, it preferably has a MgO content of about 40% to about 43.5% by weight.
The solid solution prepared as described above is an aqueous slurry and the dry powder is obtainable by removal of water from the second slurry. The resulting solids may be micronized to provide particles having a particle size distribution wherein at least 99% of the particles are less than 44 microns in diameter, and at least 95% of the particles are less than 10 microns in diameter.
The process need not be run in the presence of a surface active agent, in which case an aqueous slurry comprising an aluminum compound, preferably basic aluminum carbonate gel and/or aluminum hydroxide, and a magnesium compound, preferably basic hydrated magnesium carbonate and/or magnesium oxide, wherein the molar ratio of magnesium to aluminum is about 1.5 to 2.75, is heated to a temperature of about 70xc2x0 C. to about 95xc2x0 C. and for a reaction time xe2x80x9cXxe2x80x9d to provide a first slurry. The reaction time xe2x80x9cXxe2x80x9d is a period of time sufficient to achieve removal of substantially all free and loosely bound carbon dioxide from the aqueous slurry. The first slurry is then heated to a temperature of about 125xc2x0 C. to about 140xc2x0 C. for about 1 to about 4 hours.
The solid solutions formed by the above processes preferably have an IR spectrum which displays a split absorption band in the region of 1415-1480 cmxe2x88x921, and preferably have a crystallite size in the  less than 003 greater than  direction of about 190 xc3x85 to about 225 xc3x85.